1. Field
The disclosure relates generally to a voltage reference circuit and, more particularly, to a voltage reference circuit device for a high precision thereof.
2. Description of the Related Art
Voltage reference circuits are a type of circuit used in conjunction with semiconductor devices, integrated circuits (IC), and other applications. Voltage reference circuits can be classified into different categories. These can include (a) bandgap reference circuits, (b) circuits based on MOSFET transistor threshold voltage differences, (c) MOSFET threshold voltage and mobility compensated circuits, (d) current mode circuits, and (e) MOSFET beta multiplier networks.
FIG. 1 is an example of a prior art circuit 100 with ground (e.g. VSS) 101, and negative power supply VCC 102. The n-channel MOSFET devices T1 110 and T2 120 are used as reference MOS transistors. The transistor T3 130 is a MOSFET device with an n-type doped MOSFET gate structure. N-channel MOSFET T2 120 also has a long MOSFET channel. The MOSFET T3 130 current is “mirrored” by the current mirror formed by the two MOSFET devices T4 140 and T5 150. The current mirror formed by p-channel MOSFET devices T4 140 and T5 150 adjusts itself to the value corresponding to the cross-point of the characteristics of MOSFET device T1 110 and MOSFET device T3 130. The MOSFET devices T7 170, T8 180 and T9 190 establishes a second current mirror network which forces equal currents through the MOSFET devices T1 110 and T2 120. To initiate the start-up of the circuit, n-channel MOSFET device T6 160 conducts current when the power supply is switched on, which is provided by a positive gate voltage from the capacitor C 103. The leaky poly-silicon diode D 104 discharges through the capacitor C 103 and cuts off the n-channel MOSFET device T6 160. This circuit works properly when the power supply voltage exceeds VCC>1.5V. The prior art needs six MOSFETs, T1 110, T2 120, T5 150, T7 170, T8 180, and T9 190. In order to get a high precision output voltage, the electrical properties of these devices must have precise matching. To achieve accurate matching characteristics, the transistors must be large to minimize semiconductor manufacturing variation (e.g. photolithography and etch variations, across chip linewidth variation (ACLV), and material changes). Additionally, transistors T1 110 and T2 120 have threshold voltage variations and mismatch which leads to a voltage reference difference due to the voltage difference of each drain voltage. The disadvantages of this implementation to achieve a voltage reference circuit with high precision is the number of transistors, the physical size of the transistors, chip area, and cost.
U.S. Pat. No. 7,564,225 to Moraveji et al describes a voltage reference circuit that utilizes a work function difference between p+ gate and n+ gate to generate a pre-determined reference voltage. Additionally, the pre-determined reference voltage can be pre-adjusted using gate materials with different work functions.
U.S. Pat. No. 7,727,833 to Dix describes a voltage reference from an operational amplifier having identical PMOS transistors with each having a different gate dopant. The difference between the two threshold voltages is then used to create the voltage reference equal to the difference. The two PMOS transistors are configured as a differential pair.
U.S. Pat. No. 8,264,214 to Ratnakumar et al shows a low-voltage reference circuit which has a pair of semiconductor devices. Each semiconductor device may have an n-type semiconductor region.
In the previously published article, “MOS Voltage Reference Base on Polysilicon Gate Work Function Difference,” IEEE Journal of Solid-State Circuit, Volume SC-15, No. 3, June 1980, a voltage reference circuit is discussed that operates on MOSFET gate work-function differences.
In the previously published article “CMOS Voltage Reference Based on Gate Work Function Differences in Poly-Si Controlled by Conductivity Type and Impurity Concentration,” IEEE Journal of Solid-State Circuit, Volume 38, No. 6, June 2003, the voltage reference circuit operates on differences in the conductivity and impurity concentration.
In these prior art embodiments, the solution to improve the operability of a low voltage reference circuit utilized various alternative solutions.
It is desirable to provide a solution to address the disadvantages of operation of a voltage reference circuit.